Q&A: That glazed expression is your cue to change the subject

By Robert Matthews

12:01AM GMT 16 Feb 2005

What's happening when someone's eyes glaze over? F Gibson, Widnes

As somebody afflicted by an interest in science, I have seen more than my fair share of eyes glaze over, and take it as a cue for moving the discussion on to far more important issues, such as house prices. Regrettably, it seems the eyes of the person I contacted at the Royal College of Ophthalmologists must have glazed over when I put Mr Gibson's question to her, as she never got back with an answer.

I had more luck with Dr Fiona Rowe of the University of Liverpool and the British and Irish Orthoptic Society, who tells me that the "glazed" look is the result of a change in direction of fast eye movements or saccades, which are linked to attention.

During a conversation, our eyes range over the face of the person we're listening or talking to, to pick up hints of what they might be thinking. People who lose interest in the conversation couldn't care what the other person thinks, and so their eyes no longer dart about looking for clues.

Dr Rowe adds that while the eyes might look absolutely fixed, they never are. Tiny saccades are constantly present. Even so, the loss of the larger movements is a sign that it's time to shut up and talk about house prices.

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As stainless steel is an alloy of various metals, it is still mostly iron - so why does it not respond to magnets in the same way as the pure stuff? According to Prof John Campbell, an expert on the properties of metals at the University of Birmingham, the explanation lies in the way that the atoms in the alloy pack themselves together.

The packing is linked to the orbit and spin of the electrons in the atoms and how they respond to magnetic fields. For example, the expensive kind of stainless steel used to make kitchen pots and pans is typically a mix of iron plus 18 per cent chromium and eight per cent nickel. In this combination the atoms are packed tightly together, so that their electrons respond only reluctantly to magnetic fields.

Prof Campbell adds that cutlery is often made from a cheaper but harder stainless steel containing no nickel at all and is only 12 or 13 per cent chromium, which is just enough to keep it stainless. This leads to a more open arrangement of atoms, whose electrons respond more readily to magnetic fields.

Why is time not measured in metric units? G Willis, London

Sheer force of habit, as far as I can tell. Astronomers certainly have no qualms about it, and routinely use metric time because it makes calculations a whole lot easier. For example, the timing of celestial events are stated in terms of the so-called Julian Date (JD), a decimal time system invented by the French scholar Joseph Justus Scaliger in 1582. This converts all times to the number of days (and fractions thereof) that have elapsed since noon GMT on January 1, 4713BC. So, for example, the arrival of the Huygens probe on Titan at 10:30 GMT on January 14 has a JD of 2453384.9375.

While metric time has been adopted by astronomers, it has never caught on generally. In 1793, the leaders of the French Revolution decreed that time, like all other physical measurements, be stated in metric units. It proved so unpopular that the move was suspended barely 18 months later.